Trout Studies Seek Superior
Strains

Rainbow trout that flourish on grain-rich feed could be a plus
for the environment and fish farmers alike. Fish geneticist Kenneth E. Overturf
has pinpointed families of captive rainbow trout that thrive on grain.

Todays fish feeds, the fish farmers biggest expense,
are made with fishmeal from saltwater species such as anchovy, menhaden, jack
mackerel or herring. Using more grain in fish feed would help prevent
overfishing of these saltwater species.

Also, captive fish that gain weight when fed grain specially
bred by ARS research geneticist Victor Raboy, based in Aberdeen, may help
sidestep phosphorous pollution of ponds, lakes, streams and rivers. Phosphorous
pollution has been blamed for algal blooms that steal the oxygen needed by
fish, insects and other aquatic dwellers.

Raboy has developed barley and other grains that contain less
phytate, a form of phosphorous that is difficult for fish to digest. That means
these fish excrete less phosphorous in their manure. Trout fed the special
grains could also save fish farmers money, because grain is currently less
expensive than fishmeal.

In all, Overturf has monitored growth of about 14,000 trout in
tanks at the Hagerman station. He found that a significant percentage prospered
on the grain-enriched feed. Some grew to a hefty 250 grams in as little as five
months, making them equal in size to the biggest of their fishmeal-fed
counterparts. Overturf and ARS technician Dan Bullock are now looking at trout
DNA for a reliable indicator of the ability to gain weight and stay healthy on
grain-based feed.